Chemical measurements — AQA GCSE Chemistry
Test yourself on Chemical measurements with AQA GCSE practice questions.
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Chemical measurements explained
When you repeat a measurement, the results form a distribution.
Read the full explanation
Plot them, for example as a dot plot or a small bar chart, to show how they cluster around the mean. The mean is the sum of the measurements divided by the number of measurements. The range is the difference between the highest and lowest values. A simple estimate of uncertainty is half the range, often written as ± half the range about the mean. For example, if four titres are 24.10 cm³, 24.20 cm³, 24.15 cm³ and 24.30 cm³, the mean is 24.19 cm³ and the range is 0.20 cm³, so the uncertainty is about ±0.10 cm³. A smaller range usually indicates more precise measurements.
Your focus
- Calculate the mean and range of a set of repeated measurements.
- Estimate uncertainty as half the range about the mean.
- Represent a distribution of results using a table, dot plot or bar chart.
Chemical measurements exam tips
Marking Points
- Calculate the mean of a set of repeated measurements.
- Find the range by subtracting the lowest value from the highest value.
- Estimate uncertainty as half the range about the mean.
- Represent the distribution of results using a suitable table, dot plot or bar chart.
- Compare the spread of results to comment on the precision of the measurements.
Examiner Tips
- 💡Show the mean calculation clearly, including the sum and the number of measurements.
- 💡Write the uncertainty as a value with the same unit as the measurements, for example ±0.10 cm³.
- 💡Use a dot plot or bar chart to make the spread of results visible.
Common Mistakes
- Dividing the range by the number of measurements instead of by two; correct this by using half the range as the uncertainty estimate.
- Forgetting to include the correct unit with the mean, range or uncertainty; correct this by carrying the unit through every step.
- Plotting the mean as a single value without showing the spread; correct this by representing all individual results in the distribution.